The specific aims of the two proposed studies are to determine the: (1) effects of improvement in occlusion, vertical dimension, retention and stability of poorly fitting dentures and of new dentures upon masticatory performance, qualitative and quantitative measures of emg activity of masseter muscles and patient satisfaction; (2) relationships among masseter muscle effort, emg silent periods, masticatory performance and patient satisfaction; and (3) patterns of chewing in terms of particle size selectivity in denture wearers with good and poor masticatory performances. In Study I, 80 denture wearers would be selected from 250 subjects to represent two subgroups, one with superior and the other with poor masticatory performance based upon a standard test with peanuts. In addition to subjective data related to patient and denture characteristics, each participant would perform a series of masticatory performance and swallowing threshold tests including emg recordings of masseter muscles, force measurements and emg silent period recordings at two sittings, one week apart. Besides comparisons of masticatory performance, emg activity and criteria of patient satisfaction, the particle size distributions of food would be analyzed to discern any differences in the chewing process with respect to selectivity of particle size. Additional denture wearers may be added to those with poorly fitting dentures from Study I in order to achieve a minimum of 30 patients having completed the entire series of tests in Study II. Each participant would perform the same tests as in Study I before and after each of four denture modifications are made to improve the occlusion, vertical dimension, retention and stability of their old dentures, as well as at three time intervals after the insertion of new dentures. A three-week adaptation period would be given for each denture modification. The influence of denture modifications on masticatory performance, emg activity and patient satisfaction wold be calculated and compared with that achieved by new dentures. A computer based emg analysis system and a reliable method to relocate electrodes across sittings have been developed. Such functional assessment is needed to detemine whether or not low cost denture modifications of old dentures provide functional efficacy to merit their use over high cost denture remakes. Our long term goal has been to improve denture designs and treatment procedures which would increase functional effectiveness and comfort of dentures and reduce the cost of services.